L0301P106 - Principles of Lymphatic System
Lymphatic Systems *part of the circulatory system and a vital part of the immune system *complex network of capillaries, thin vessels, valves, ducts, nodes and organs *carry lymph directionally towards the heart via lymph nodes for filtration Lymphatic Drainage Thoracic Duct *at its origin - duct drains lymph from almost the entire body below the diaphragm *at its termination i- duct drains lymph from the left upper quadrant Right Lymphatic Duct *major direct pathway for drainage of the right upper quadrant (white) **right upper limb, right side of head, neck, chest and abdomen wall Trunks *head, neck, upper limb and thorax —> jugular, subclavian, bronchomediastinal *abdomen, pelvis, and lower limb —> intestinal and lumbar trunks Histology *lymphatic vessels are difficult to locate and identify *have: **valves to ensure unidirectional movement **no connective tissue in the wall **no smooth muscle (unlike blood vessels) **incomplete basement membrane under the endothelium Functions of the Lymphatic System Physical Role *drainage of extracellular tissue fluid *filtering of extracellular tissue fluid Immunological Role *early and efficient warning of invaders *recognition of foreign antigens *production of antigen specific cells **B cells -> plasma cells **various subtypes of T cells *swelling of lymph nodes indicates infection or cancer Clinical Examples *small infection of skin of hand (streptococcus) causing red lines runs slowly up the arm to armpit (axilla) *lymphangitis **inflammation of the lymph vessels *lymphadenitis **swelling under armpit of lymph nodes *breast cancer **enlargement of axillary lymph nodes *infections of throat, lymphoma **swelling of nodes of neck **very painful, change in voice *subcutaneous injections **reaches nodes within minutes Tissue Fluid *produced in capillary beds *extracellular fluid that does not return to venous system **mainly water, low in cells and leukocytes, lower protein content than plasma *present in all tissues of the body except: **avascular tissues ***cartilage, cornea, nails, hair **some vascular tissues - brain and eye which share unique blood-tissue barriers  Formation #blood travels to arterial capillaries #interstitial fluid (tissue fluid) formed at capillaries by hydrostatic pressure from the left side of the heart #interstitial fluid bathes cells and tissues *acts as conduit to allow diffusion of O2 and CO2 #some is reabsorbed into venous capillaries due to osmotic pressure #not all tissue fluid is reabsorbed, some goes into the lymphatics - called lymph Lymphatic Capillary *lymphatic capillary has poorly developed basal lamina (basement membrane) *devoid of pericytes *endothelium is highly attenuated *cells are connected directly to the interstitial collagen via anchoring filaments (AF) *cells can move in and out of them easily **T, dendritic, antigen presenting cells Lymphatic Circulation *all fluid is recycled to the systemic vascular system via the venous system *most lymphatic channels have no smooth muscle but do have valves **unidirectional flow —> towards the nodes and heart *muscle activity, adjacent artery pulses, pressure in compartments allow return to the vascular system *measures to avoid and treat lymphedema **compression garments, bandages, exercises, massage, Lymph Node Filtration *all fluid in lymphatic capillaries is filtered through at least one lymph node *cells in lymph node which **remove cell debris - by phagocytosis **filter foreign particles - by phagocytosis **recognise foreign proteins - lymphocytes **basis of immunological memory in adaptive immune system *T lymphocytes **proliferate and become activated if they encounter antigen elsewhere in body *B cells **plasma cells **produce antibody specific to the antigen Lymph Nodes *bean-shaped structures *organisation has been adapted to maximise opportunity for antigens in lymph to encounter **T cells in cortical zone **B cells in medullary zone *acts as a ‘settling tank’ - subcapsular sinus **macrophages trap and phagocytose debris and/or pathogens *lymph enters via afferent vessel and leaves via efferent vessels *nodes have a rich blood supply **many cells enter and leave the node *more numerous close to ‘portals of entry’ **skin, respiratory tract, GIT, urogenital tract Levels of Lymphatics *superficial **follows veins **drains the skin **greatest percentage of lymph drainage *deep **follows arteries **less frequent but critically important *lymphatic plexus **allows lymph to take several pathways **pathways may differ in pathological situations ***hence tumour spread may not always follow same pattern   Lymphoid Organs *substantial collections of lymphoid tissue *thymus **site of T-cell maturation, active until puberty (after - involutes and shrinks) *spleen **filters blood, removes old and damaged blood cells **breakdown products transported to the liver for excretion in bile General Pathway *superficial capillaries —> deep capillaries —> afferent lymphatics —> lymph node (superficial to deep) —> efferent lymphatics —> trunk —> duct —> venous system